Python datetime format: UTC time zone offset with colon

Question

I'm trying to format a datetime object in Python using either the strftime method or an f-string. I would like to include the time zone offset from UTC with a colon between the hour and minute.

According to the documentation, a format code, %:z, may be available to do exactly what I want. The documentation does warn, however, that this may not be available on all platforms.

I am running Python 3.10 on Windows, and it doesn't seem to work for me. I guess I'm wondering if I just have the syntax mixed up or if indeed this format code isn't available to me. Anyone else have experience with this?

The following statement raises a ValueError: Invalid format string:

print(f"{datetime.now().astimezone():%Y-%m-%d %H:%M:%S%:z}")

Using the %z format code instead of the %:z code does work, however, giving me something close to what I want, namely 2024-10-09 13:17:21-0700 at the time I ran it:

print(f"{datetime.now().astimezone():%Y-%m-%d %H:%M:%S%z}")

The problem with strftime is that it relies too much on the operating system instead of implementing it itself. — Mark Ransom
– Mark Ransom, Commented Oct 9, 2024 at 20:53
@MarkRansom That would seem to be the case. I don't suppose there's a good alternative in the Python standard library? Right now I suppose I'll just use %z and slice and splice the resulting string to insert the missing colon. — E_Cross
– E_Cross, Commented Oct 9, 2024 at 21:00

Mark Tolonen · Accepted Answer · 2024-10-09 22:53:41Z

3

Per documentation:

Added in version 3.12: %:z was added.

Example on Windows 10:

Python 3.12.6 (tags/v3.12.6:a4a2d2b, Sep  6 2024, 20:11:23) [MSC v.1940 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import datetime as dt
>>> print(f"{dt.datetime.now().astimezone():%Y-%m-%d %H:%M:%S%:z}")
2024-10-09 15:46:13-07:00

Pre 3.12, you could make a helper function:

import datetime as dt

def now():
    s = f'{dt.datetime.now().astimezone():%Y-%m-%d %H:%M:%S%z}'
    return s[:-2] + ':' + s[-2:]

print(now())

Output:

2024-10-09 15:52:51-07:00

edited Oct 9, 2024 at 22:53

answered Oct 9, 2024 at 22:46

Mark Tolonen

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1 Comment

E_Cross Over a year ago

Ah, how silly I was. I thought I was looking at the documentation for Python 3.10 when I saw that %:z was an option, but evidently I got things mixed up and it's only available starting with 3.12.

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